In some aspects, this invention generally relates to scrubbers used to remove matter (e.g., particulate, gaseous, or liquid) from a gas stream in order to recover the matter and/or to clean the gas. In particular aspects, this invention relates to a positioning of multiple venturis that may provide additional flexibility and increased efficiency. The invention also pertains to related methods.
Scrubbers—such as those described in U.S. Pat. Nos. 5,279,646; 5,484,471; 5,512,085; and 5,759,233—are known. FIG. 1 of U.S. Pat. No. 5,512,085, for example, shows an example of extant technology.
This system of the '085 patent is quite simple. Gas enters the venturi portion of the scrubber (on the left) where a liquid is sprayed in to the throat of the venturi. In many instances, the diameter of the venturi throat can be approximately 12″ to 48″.
The purpose of the venturi is to impact the liquid with the matter to be removed. The liquid is then separated from the gas through impact with a liquid level at the bottom of the venturi, and through centrifugal forces in the separator vessel (on the right). There can be a demister at the top of the separator vessel, or external to the separator vessel, to remove any residual liquid droplets.
An advantage of this technology is that it can be very inexpensive. A disadvantage is that it may not be efficient enough to meet gas cleanliness standards set by regulatory agencies. Another disadvantage is that a high pressure drop across the venturi may be required to achieve high efficiency, which costs the mill energy and possibly equipment upgrades.
Other scrubbers are also known. For example, FIG. 1 shows a scrubber that is quite different than the ones mentioned above.
In FIG. 1, the inlet 10 is not a venturi, but rather a duct with spray nozzle(s) 12 used to quench the gases to saturation. In this illustrated device, there are multiple venturis 30 positioned within the separator vessel 20, each with its own spray nozzle 32. These venturis may have throats with a diameter of between 6″ and 12″. In a preferred embodiment, the venturi may have a throat of approximately 8″. There may be a preliminary cleaning step (shown by sprayer 42) and demister(s) 40, as shown in this figure.
An advantage of this system is that it may be highly efficient at a low pressure drop. A disadvantage is that it may be very expensive relative to a system with an external venturi. Another disadvantage is that it may require modification to an existing (e.g., older) vessel in the case of a retrofit project.
In light of the above-identified deficiencies of the prior art, there exists a need for an improved scrubber, particularly a scrubber that enables a good efficiency and reasonable pressure drop.
In certain embodiments, the multiple venturis of the present invention may provide flexibility in scaling up and scaling down the separation process, thus enabling a wider range of operating parameters, process conditions, and loading. The multiple venturis may also facilitate repairs, as each venturi unit may be replaced, repaired, or reconstructed individually. This flexibility may not only reduce downtime, but may also provide flexibility in designing, testing, and evaluating new configurations and devices. Furthermore, at least certain embodiments of the present invention are particularly suitable for relatively inexpensive retrofits to existing equipment.